a) Field of the invention
The present invention relates to a zoom lens system which has a short total length and is suited for use especially with lens shutter cameras, etc.
b) Description of the prior art
As the conventional zoom lens system which has a range of field angles covering the standard field angle (on the order of 2.omega.=47.degree.) and a vari-focal ratio on the order of 2, and is designed so compact as to be built in the lens shutter cameras, there is known the zoom lens system composed of a front lens unit having a positive refractive power and another lens unit having a negative refractive power.
This zoom lens system is characterized in that it has a composition similar to that of the telephoto type lens system, thereby permitting shortening the total length thereof. As a conventional example of the zoom lens system having the composition described above, there is known the lens system disclosed by Japanese Patent Kokai Publication No. Sho 64-52111 (U.S. Pat. No. 4,838,669) which has aberrations corrected with good balance and a shortened total length.
This type of zoom lens system has a short back focal length and comprises a rear lens unit located close to the image surface, thereby having a defect that the lens components arranged in the rear lens unit have large diameters. Speaking concretely, the lens components arranged in the rear lens unit have diameters which are approximately twice as large as those of the lens components arranged in the front lens unit, thereby enhancing manufacturing cost of the lens components arranged in the rear lens unit.